Hydrophilic refers to the ability to "wet-out" a liquid. "Wet-out" refers to the ability to cause a liquid (e.g., an aqueous solution) to penetrate more easily into, or spread over the surface of another material. Generally, polyolefins are considered hydrophobic. Hydrophobic refers to the inability to "wet-out" a liquid.
Various methods to make polyolefins more hydrophilic generally include: coating with a surfactant (or surface active agent or wetting agent); coating with a polymer(s), the polymer(s) having different (i.e., better) surface active properties than the polyolefin; surface activation (e.g., by plasma treatment); surface roughing to increase surface area (e.g., foaming the surface); and blending the polyolefins with another polymer(s), the blend having different (i.e., better) surface active properties than the polyolefin. Examples of the foregoing are illustrated in Japanese Kokai Nos.: 2-133608 (published May 22, 1990); 2-133607 (May 22, 1990); 3-55755 (Mar. 11, 1991); 4-346825 (Dec. 2, 1992); and 5-106112 (Apr. 17, 1993); and European Patent Publication Nos. 498,414 A2 (Aug. 12, 1992); 634,802 A1 (Jan. 18, 1995); and 203,459 A2 (Dec. 3, 1986).
In the foregoing methods, the hydrophilicity of the polyolefin may degrade over time. Accordingly, there is a need for a permanently hydrophilic polyolefin.